Method of monitoring status of a silicon layer by detecting, emission spectra variable during etching

Abstract

In a monitoring method of monitoring status of a silicon layer etched in a hollow space by plasma, a chlorine including gas is introduced into a hollow space to cause CCl-radical to occur in the hollow space. A first spectrum region is selected to detect first emission spectra of the CCl-radical which are variable in intensity only during the etching and which may include a wavelength of 307 nm. Preferably, a second spectrum region is selected to second emission spectra invariable even during the etching and to indicate the beginning and the end of the etching by monitoring a relationship between the first and the second emission spectra. The second spectrum region may include a wavelength of 396 nm. Alternatively, emission spectra of OH-radical which results from water remaining in the hollow space may be monitored as the first emission spectra.

What is claimed is: 
     
       1. A method for use in etching a layer of silicon by plasma in a chlorine including gas filled in a hollow space, to distinguish between a first and a second duration which said layer is being etched and not, respectively, said plasma producing CCl- and OH-radicals whch result from said chlorine including gas and from water remaining as a remnant in said hollow space, respectively, said method coprising the steps of: selecting emission spectra which result from a preselected one of said CCl- and said OH-radicals and which are variable in intensity at a transition time instant between said first and said second durations; and   monitoring said intensity of said emission spectra to detect said transition time instant and to, thereby, distinguish between said first and said second durations.   
     
     
       2. A method as claimed in claim 1, wherein said preselected radical is said OH-radical, the emission spectra of said OH-radical being laid in a predetermined spectrum region. 
     
     
       3. A method as claimed in claim 2, wherein said predetermined spectrum region includes a wavelength of 307 nm. 
     
     
       4. A method as claimed in claim 1, wherein said preselected radical is said CCl-radical, the emission spectra of said CCl-radical being laid in a prescribed spectrum region. 
     
     
       5. A method as claimed in claim 4, wherein said prescribed spectrum region includes a wavelength of 307 nm. 
     
     
       6. A method as claimed in claim 1, wherein said chlorine including gas comprises carbon tetrachloride. 
     
     
       7. A method as claimed in claim 6, wherein said chlorine including gas further comprises at least one additional gas selected from a group consisting of inert gases, an oxygen gas, and a nitrogen gas. 
     
     
       8. A method as claimed in claim 7, wherein said additional gas comprises a helium gas. 
     
     
       9. A method as claimed in claim 8, wherein said additional gas further comprises said oxygen gas. 
     
     
       10. A method as claimed in claim 1, wherein said layer comprises polycrystalline silicon. 
     
     
       11. A method as claimed in claim 10, wherein said layer comprises at least one of phosphorus, boron, and arsenic doped in said polycrystalline silicon. 
     
     
       12. A method as claimed in claim 1, further comprising the step of: further selecting additional spectra invariable in intensity at said transition time instant;   said monitoring step comprising the steps of:   detecting a relationship between the intensities of said emission spectra and said additional emission spectra; and   distinguishing between said first and said second durations in consideration of said relationship.   
     
     
       13. A method as claimed in claim 12, wherein said additional emission spectra comprises a spectrum region including a wavelength of 396 nm.